1. Field of the Invention
The present invention relates to a camera capable of finding an aperture value and/or a shutter speed by computations based on the result of a light measurement and provided with lock means for maintaining the settings obtained by the computations.
2. Description of the Related Art
A number of proposals have heretofore been made with respect to the way in which exposure is controlled when a camera is switched from one photographic mode to another with an AE lock being set (AE lock serves to lock an aperture value and/or a shutter speed computed on the basis of the result of a light measurement). In one proposed system, if a photographer switches a camera from one photographic mode to another, the AE lock of the camera is cancelled to clear all the AE values, and the camera is placed in a standby state. When the photographer operates the camera to again perform a light measurement, the AE lock is applied to the result of the light measurement in response to an in-focus signal or a lock signal associated with a manual operation, and exposure control based on the AE lock is performed.
In another proposed system, if a camera is switched from one photographic mode to another, the AE lock of the camera is cancelled to clear all of the AE values. Then, a light measurement is again performed automatically and new AE values are found by using an exposure computing formula according to the selected photographic mode. The AE lock is applied to the new AE values and exposure control based on the AE lock is performed.
However, in the former system, if the camera is switched from one photographic mode to another, the AE lock which has been intentionally applied to the AE values by the photographer is completely cancelled, so that a photographic intention which the photographer had when the AE lock was first set will be ignored. In addition, since the photographer must set the AE lock again, the operability of the camera is impaired.
In the latter system, if the camera is switched from one photographic mode to another, the AE lock is again set automatically. More specifically, after all the AE values are cleared, a light measurement is again performed to obtain updated the AE values and AE lock is applied to the updated AE values. An actual exposure result will, therefore, differ from the exposure that the photographer had intended when the AE lock was set, with the result that the photographic intention of the photographer will be ignored.
For example, a conventional exposure control device for a camera capable of setting AE lock in response to either of in-focus and lock signals is arranged to operate as shown in FIG. 7. As shown, even if there is a result of a light measurement to which the AE lock has previously been applied in response to an in-focus signal (Step Group #1), if a lock signal is outputted in response to a manual operation, a light measurement is again performed to update the AE values and the AE lock is applied to the updated AE values (Step Group #2). On the other hand, if there is a result of a light measurement to which the AE lock has previously been applied in response to a lock signal (Step Group #3), even if an in-focus signal is outputted, the AE values remain locked and are not updated (Step Group #4), that is to say, the lock signal has priority over the in-focus signal. When a release button is depressed to a second stroke position, exposure of film is executed in accordance with an aperture value and a shutter speed which have been locked by any one of the aforesaid AE lock operations, and the film is then transported (Step Group #5).
However, the above-described conventional example which shown in FIG. 7, still has a number of disadvantages. In the above-described sequence including the steps of locking AE values in response to an in-focus signal, updating the AE values in response to a lock signal and locking the updated AE values, if a photographer presses the release button unintentionally or accidentally so that a lock signal is outputted, the desired AE values are updated and AE lock is applied to the updated AE values. As a result, exposure control is executed which differs from the intention of the photographer.